They admitted the sanctions would be partly symbolic but said it was important to name mid-level government officials to show there could be consequences for their actions.

In its response on Thursday North Korea urged Washington to withdraw the sanctions immediately.

It vowed to instantly cut off all diplomatic channels if they failed to do so.

The North Korean statement said: "The United States has dared to challenge the highest authority of ours, committing the worst-ever hostile act that goes beyond confrontation over the so-called human rights issue. This constitutes an open declaration of a war.

"Now that the US has made a declaration of a war against us all issues arising from relations with the US will forthwith be handled in accordance with our wartime laws."

The US move was welcomed by South Korea which cut off all political and commercial ties under its own sanctions in February.

China has opposed unilateral sanctions and claimed that the human rights situation in North Korea is not a threat to international peace and security.

It has sought to prevent the issue being discussed at the UN Security Council.

John Kerry, the US Secretary of State, said: "China's engagement is critical. Our hope is that we continue to cooperate as we have been in the last months."

A UN spokesman said: "The Secretary-General believes that discussion of human rights concerns allows for a more comprehensive assessment and action when addressing security and stability concerns on the Korean Peninsula."